

ABSTRACT

A particle sorting method and apparatus for separating minute particles incorporated in a liquid stream in accordance with selected particle parameters. Particles such as biological cells to be separated are incorporated in the inner or central portion of a confined coaxial flow stream which includes an outer cell-free fluid sheath portion. This coaxial flow stream is released through a vibrating nozzle for inspection by one or more cell sensing means for sensing cells in the jet stream immediately downstream of the nozzle. Beam illumination and/or observation of the jet stream for particle sensing is effected outside of the nozzle. Vibration of the nozzle breaks the coaxial jet stream into a series of uniform drops downstream of the cell sensing means, and signals from said means are used to initiate delayed charging pulses applied to preselected cell-containing drops as they break from the vibrating fluid jet. Nozzle vibration is synchronized with the charging pulse to prevent separation of drops from the stream during the drop charging pulse on and off transition times, thereby preventing undesired drop charging. The drops pass between charged deflection plates where the charged drops are deflected into appropriate receptacles. By using a plurality of sensing means such that all cells are sensed by one sensor, and only certain cells, i.e. cells characterized by a particular parameter value, are sensed by another sensor, drops containing both cells characterized by a particular parameter and cells not characterized by that parameter can be sorted away from the receptacle for cells characterized by that particular parameter.



